Asymmetric Talbot-Lau interferometry for inertial sensing

Abstract

We study in detail a peculiar configuration of the Talbot-Lau matter wave interferometer, characterized by unequal distances between the two diffraction gratings and the observation plane. We refer to this apparatus as the "asymmetric Talbot-Lau setup." Particular attention is given to its capabilities as an inertial sensor for particle and atomic beams, also in comparison with the classical moiré deflectometer. The present paper is motivated by possible experimental applications in the context of antimatter wave interferometry, including the measurement of the gravitational acceleration of antimatter particles. Therefore we focus our analysis on the current state of the art. To support our findings, we have also performed numerical simulations of realistic particle beams with varying speed distributions.

First demonstration of antimatter wave interferometry

“…It exploits an intermediate working regime between the standard Talbot-Lau setup, where the two gratings and the detector are equally spaced, and the so-called Lau interferometer ( 27 ), which has more stringent coherence requirements ( 25 ). By means of unequal grating periodicities, the system provides sizable period magnification in a relatively compact setup ( 21 ). In particular, we used gold-coated 700-nm-thick silicon nitride (SiN) gratings with periodicity d 1 = (1.210 ± 0.001) μm and d 2 = (1.004 ± 0.001) μm to produce a d 3 = (5.90 ± 0.04) μm periodic interference pattern.…”

“…Interferometer alignment is particularly challenging, and it is intimately connected to beam coherence. The Talbot-Lau interferometer can produce high-contrast fringes if the resonance condition ( 21 )L1L2=d1d2−1is met, even for a fully incoherent ( l → 0) beam. However, as this regime is approached, the required accuracy at which the above condition should be ensured increases.…”

“…The apparatus operated at a vacuum pressure between 10 −7 and 10 −6 mbar during each measurement. We configured the interferometer for maximum contrast at E = 14 keV (λ dB = 10.3 pm) by setting L1=d1d2λdB ( 21 ). Since this geometry satisfies the Talbot-Lau resonance conditions, single-slit diffraction from the first to second grating plane is not negligible (as it would instead occur for L1λdBd1≪d2).…”

“…The measured contrast modulation is in fair agreement with the expected behavior for a Talbot-Lau interferometer and is incompatible with classical moiré deflectometry ( 33 ), where particles propagate on ballistic trajectories through the gratings. Since this geometry could, in principle, produce a fringe pattern with the same periodicity from geometrical shadow effects alone ( 21 ), this conclusion holds only if spurious energy-dependent effects are ruled out. A possible source could be the energy-dependent positron transmission from the grating bars, which varies from about 0.1% at 8 keV to 49% at 14 keV.…”

Progress toward a large-scale ion Talbot-Lau interferometer

“…A device which operates in these conditions is commonly referred to as the moiré deflectometer [13][14][15]. For specific configurations satisfying L = nL T , with n ∈ Z + , the Talbot-Lau interference pattern is indistinguishable from the corresponding classical pattern [16,17]. The ideal configuration to reveal the wave behavior of the test particles is therefore not at this resonance condition.…”